Surface wave dispersion beyond cutoff for a fast layer on a slow substrate

Abstract

The velocity and attenuation of pseudosurface waves beyond cutoff have been calculated for several layers on a slow substrate and unexpectedly different kinds of behavior can be distinguished. When the elastic properties of the layer and the substrate are not very different, the velocity of the pseudosurface wave beyond cutoff increases up to the Rayleigh wave velocity of the layer. When the elastic properties of the two materials are quite dissimilar, the pseudosurface wave tends towards an attenuated interfacial mode. In addition, another mode appears evolving into the Rayleigh wave of the layer material.

Repulsion of resonance states and exceptional points

“…A level repulsion in the complex energy plane can appear as a crossing of, say, their real parts, since the corresponding imaginary parts still can avoid each other; likewise, a genuine repulsion of the real parts can imply a crossing of the imaginary parts. These aspects have been discussed in a variety of contexts: in nuclear and particle physics, for electro-magnetic resonators [1,2] and in results found for absorptive media in solid state physics [3]. An investigation on a more theoretical footing is found in [4].…”

<title>Elastic properties of cBN films by surface Brillouin scattering</title>

“…This peak is associated with leaky or pseudo SAW (PSAW) [15]. As θ or kh increase, the PSAM is transferred into leaky interface wave [9,15]. In the same spectral region, another broad peak appears, which with increasing θ becomes narrower, as the associated mode tends towards the Rayleigh mode of cBN.…”

“…V FT is the fast transverse velocity in the substrate. This peak is associated with leaky or pseudo SAW (PSAW) [15]. As θ or kh increase, the PSAM is transferred into leaky interface wave [9,15].…”

“…Theoretical consideration of the SAW behavior for hard films [15] shows that the SAW velocity initially grow with increasing kh, where k is the wave number of SAW and h is the thickness of the film. At a critical value kh cut the SAW meets shear wave and degenerates with the bulk wave continuum (cut-off point).…”

Behaviour of surface phonons in LiCsSO4 crystal at phase transition

“…The method of Brillouin spectroscopy permits determination of bulk and surface elastic properties of the materials studied. The elastic properties of the real solid state surfaces, being significantly different from the bulk elastic properties, have been recently intensely studied in view of the applications in modern technologies [12][13][14].…”